1. Field of the Invention
This invention relates to novel antitumor compositions which exhibit marked antitumor action by non-injection administration. More specifically, the invention relates to novel antitumor compositions for non-injection administration each of which comprises a pharmacologically effective quantity of an ester of 1-.beta.-D-arabinofuranosylcytosine-5'-phosphate and a vehicle.
2. Prior Art
It has been known that 1-.beta.-D-arabinofuranosyl cytosine (hereinafter referred to as ara-C) is an agent which is indispensable for chemotherapy of cancers, especially leukemias such as acute lymphatic leukemia (ALL), acute myelogenous leukemia (AML) and meningo-leukemia. Recently, ara-C has been often employed in combination with other agents, for example, in DCMP (daunomycin-ara-C-mitomycin-predonisolone) therapy and MFC (mitomycin-5-fluorouracil-ara-C) therapy. Thus, the ara-C has been often used as an essential agent of combined therapeutics in the chemotherapy of leukemias as well as solid cancers such as lymphoma, gastric and intestinal cancers and adenocarcinoma (e.g., reference is made to "Chemotherapeutics of Cancers", Yakuzai Koza Vol. 1, p.p. 75-80, compiled by H. Niitani and H. Kanagami, published by Clinic Magazine Company, Japan, July 1, 1977). At the moment, however, ara-C can only be used for intravenous or intramuscular injection from a viewpoint of pharmacodynamics and actually cannot be used for oral administration. This fact has been an obstacle to further extensive applications of ara-C. Especially, its continuous administration by intravenous injection gives rise to physical and mental pain to a considerable extent in the patients. Thus, the development of forms of ara-C which can be administered orally has been urgently needed in the clinical field.
Hitherto, the syntheses of ara-C derivatives which can be administered orally have been tried (cf. J. Med. Chem. Vol. 19, No. 8, p.p. 1013-1016, 1976). It has also been reported that the oral administration of ara-C is effective in combination with a cytidinedeaminase inhibitor such as tetrahydrouridine (cf. Cancer Research, Vol. 30, p.p. 2166-2172, 1970). However, the effects are not remarkable and there has been no prospect of practical use of this administration.
On the other hand, the present inventors have synthesized alkyl or aryl esters of arabinofuranosylcytosine-5'-phosphate (hereinafter referred to as ara-CMP) in order to study improvement in so-called bioavailability of the ara-C derivatives such as their resistivity to cytidinedeaminase, their effects on ara-C-resistant strains, and their antitumor properties based on selective affinity for organs. These esters were tested with respect to their antitumor properties (cf. Reports on the proceedings of the 35th annual meeting of the Japanese Cancer Association, p. 133, No. 476, issued by Nippon Gan Gakkai, Sept. 1, 1976). The esters of ara-CMP, however, only showed a lower activity than ara-C and ara-CMP in cell proliferation-inhibition effects in vitro using L5178Y cells. Also, in the antitumor tests in vivo using mouse-leukemia cell L1210, the esters tested only showed an increase in life span similar to or lower than ara-CMP when they were administered intraperitoneally. The alkyl esters having 11 or more carbon atoms in the alkyl moiety showed some effectiveness in that the effective doses were decreased but were accompanied by an increase in toxicity. On the whole, in both in vitro experiment and intraperitoneal administration, pharmacologically useful improvements in ara-C or ara-CMP were not observed over the ara-CMP esters.
Hitherto, it has been considered that the most effective administration of a drug is generally attained by intravenous injection (or intraperitoneal injection), and the maintenance of the drug concentration in the blood at a certain level is required for the drug to exhibit effectiveness in the therapy of leukemias such as L1210 leukemia. Consequently, the ara-CMP esters which are not very effective in intraperitoneal administration have not especially been appreciated as antitumor agents.